Fluid cushioned coating method and apparatus



Jan. 30, 1962 HORNBOSTEL 3,019,130

FLUID CUSHIONED COATING METHOD AND APPARATUS Filed Oct. 2, 1958 Ill M Hm EXCESS COATING Lloyd Hornbosfe/ United States Patent 3,019,130 FLUIDCUSHIONED COA'IING METHOD AND APPARATUS Lloyd Hornbostel, Beloit, Wis,asslgnor to Beloit Iron Works, Beloit, Wis., a corporation of WisconsinFiled Oct. 2, 1958, Ser. No. 764,891 11 Claims. (Cl. 117-111) Thisinvention relates to a method of and apparatus for coating sheetmaterial. More particularly, this invention relates to such a method andapparatus wherein a mobile coating composition is smoothed upon aportion of a flexible web or sheet which is supported for the smoothingoperation by maintaining a positive gas pressure which acts as a cushionfor the web. The invention is applicable to the coating of woven orfelted fabrics, paper, sheets of rubber or other resinous material,cellulose films, and other sheet material of similar nature.

Various methods of smoothing a coating composition on a web have in thepast been developed. Some of these methods have utilized an air jet inorder to smooth coating compositions on a Web which is supported fromits opposite side either by a roller or other solid surface. One suchmethod is, for example, disclosed in US, Patent No. 2,252,345, issued toS. J. Johnson on August 12, 1941. In the prior art methods, on air jetfrom a nozzle urges the moving web against a blade and is able to applyonly the force due to the velocity energy of the air stream.Furthermore, since the air is continuously flowing and escaping to theambient, it is necessary to expend considerable energy in the continuousair pumping operation.

It is therefore an object of the present invention to provide a methodand apparatus for smoothing coating compositions on a web whichovercomes the above-noted disadvantages of the known prior art.

It is a further object of this invention to provide a method andapparatus for smoothing coating compositions on a web wherein a positivegas pressure is built up in back of a portion of the web which isdisplaced from a guide surface and urged toward a smoothing surface bythe positive pressure.

It is a further object of this invention to provide a method andapparatus for smoothing coating compositions on a web wherein the coatedweb is urged against a smoothing surface by gas under pressure which gasmay also be heated to simultaneously initiate the drying process duringthe smoothing step.

It is a further object of this invention to provide a resilient,controllable means whereby a coating applied to a web may be leveled andsmoothed either with or without the removal of excess coating and whichutilizes a substantially static positive gas pressure so that power needbe expended only to overcome gas leakage.

Other objects, features and advantages of the present invention will bemore fully apparent from the following detailed description taken inconnection with the accompanying drawing wherein:

FIGURE 1 is a diagrammatic showing of a typical apparatus suitable foruse in the present method.

FIGURE 2 is a somewhat fragmentary and schematic perspective view of theapparatus shown in FIGURE 1.

Turning to the drawings and in particular to FIGURE 1 thereof, a web 10,for example a web of paper, with its two sides indicated as A and Brespectively, is fed from any convenient source and is continuouslyadvanced through the nip of a pair of adjacent rollers 11 and 12. Theside A of the web contacts the roller 11 which turns in a vat 13containing a fluid coating composition. Roller 11 is driven by anyconvenient means (not shown) at a speed which permits the application tothe web of the desired weight of coating composition. This coating isapplied to the side A of the web 10.

Patented Jan. 30, 1962 The web 10 is then trained or fed around aperforate roller 14 so that the side B of the web contacts the surfaceof the roller 14. It will, of course, be understood that in the use ofthe device coating may be applied to the web in advance of the perforateroller 14 by any convenient means known in the art. The use of rollers11 and 12 and vat 13 for this purpose is of course shown only by way ofexample. The uncoated or reverse side B of the web is then trained orwrapped around the perforate roller 14 and the applied coating isleveled or smoothed by a blade or doctor 15 in a manner to be describedbelow. If desired, an excess of coating may be removed by the doctor 15and received in a vat 16 positioned below the doctor.

It will be noted that the roller 14 is a hollow cylindrical roller theouter cylindrical wall 17 of which is provided with a plurality ofperforations or apertures 18 which are preferably uniformly spaced overthe entire surface thereof. Inside the roller 14, a gland or housing 19is reconnected to any convenient source of a gas such as air maintainedunder a controllable pressure. The gland 19 is shown in cross-section inFIGURE 1 and preferably extends the entire axial length of the roller14. In crosssection, gland 19 may conveniently be of generally U orhorseshoe shape and is thus provided with an air outlet channel 20formed by the gland side members 21 and 22 which respectively extendinto contacting relation with the inner surface of the wall 17 of theroller 14. In practice, it is preferred to make the diameters ofapertures 18 less than the thickness of gland wall members 21 and 22.The chamber 23 formed between the outer wall surface of the gland 19 andthe inner wall 17' of roller 14 may in certain applications convenientlybe provided with an additional gland or glands connected to a vacuumsource so that the portion of the roller 14 exposed to the said gland orglands may function as a suction roll to maintain the web firmly incontact with it. The use of a moderate vacuum in suction chamber 23 is,for example, desirable where the angle of wrap of the web about theroller 14 must be less than or with light sheets or webs which may belifted by the air pressure from chamber 19 entirely away from the roller14.

As the web 10 is fed around the roller 14, a bubble 24 is formed in theportion of the web in front of the air outlet 20 from pressure chamber19. This: results from the fact that the air under pressure from chamber19 displaces the web 10 from the guide surface afforded by the outersurface of roller 14 and urges the web outwardly therefrom into contactwith the blade or doctor 15. In order to prevent any substantial escapeof air from the ends of the bubble 24 thus formed, stationary blocks ordams 25 and 26 are provided close to each. of the edges of thetravelling web. These blocks may conveniently be mounted in closelyspaced relationship to the ends of roller 14 and protrude outwardlybeyond the roller past the position of the blade 15 in order to insure acomplete closure of the ends of the bubbles. The positive air prasuremaintained in the bubble by the pressure chamber 19 urges the bubbleportion 24 of the web 10 against the doctor 15 and affords an aircushion for the web during the smoothing operation. The web is thenconducted to any known dryer arrangement such as the dryer drums of thepaper machine or tunnel dryers or the like. In FIGURE 1, this isillustrated schematically by the roller 27 over which the web 10 is fedto a dryer 28.

There is thus provided a resilient, controllable means whereby anapplied coating may be leveled and smoothed either with or without theremoval of any excess coating as desired. The force with which the web10 is urged against the blade 15 is of course determined by and may becontrolled by adjustment of the air pressure in the pressure chamber 19.The perforate roller 14 and gland 19 are similar to a suction roll inarrangement but in practice may be lighter in construction. Theconsumption of air is small because only leakage losses must be pumped.The perforate roll may be light since it is required essentially tosupport only its own weight. The air pressure which may be used islimited only by the permissible tension in the web being coated andsince the applied forces are essentially in balance there is nosignificant applied load to the roll itself. I

With certain coatings and paper combinations, the use of heated air maybe desired in order to begin the set of the coating during the smoothingoperation. This may readily be achieved by interposing any suitableheating means in the line feeding air to pressure chamber 19. As notedabove, the use of a moderate vacuum in the suction chamber 23 isfrequently desirable but is not necessary in many applications. If avacuum is not maintained in the suction chamber the web may be heldagainst the roller 14 by the normal tension in the feeding loop.

It will of course be apparent that the present method and apparatus maybe used either in a paper making machine or on independent coatingmachines of any known type. The use of a positive gas pressure to urgethe web against a smoothing surface or into a smoothing position for anysuitable type of smoothing operation affords a controllable air cushionto support the web during the smoothing operation without requiring thatlarge volumes of air be pumped. At the same time, it affords thepossibility of initiating the drying action during the smoothing actionby using heated as well as pressurized air to form the above discussedcushion.

While air is in fact used to form the cushion in the presently preferredembodiment of the invention, it will be understood that any suitable gasor fluid could equivalently be used. The term gas as used in thespecification and claims is therefore intended to mean any pumpablefluid including air which may be maintained under positive pressure,that is, under pressure greater than ambient atmospheric pressure.

While a particular preferred exemplary embodiment of the invention hasnow been described, it will be understood that modifications andvariations may be effected therein without departing from the spirit andscope of the novel concepts of the present invention as defined by thefollowing claims.

I claim as my invention:

1. A method of smoothing mobile coating composition on one side of aflexible web comprising, continuously engaging a moving surface with theopposite side of said coated web to advance said web along a pathdefined thereby, yieldably moving a limited length of said advancing webaway from said moving surface and held with its coated one side pressedagainst a rigid smoothing element by gas pressure acting across saidlimited length of said web to thereby smooth said coating composition onsaid one side of said web while it is yieldably supported by said gaspressure.

2. A method of coating an elongated flexible web with a mobile coatingmaterial comprising, applying said coating material to a side of saidweb, continuously advancing said web while the major portion of theopposite side thereof is in contact with a perforate guide surface,urging a minor portion of said web away from said guide surface bymaintaining a positive gas pressure only on said opposite side of saidweb, and smoothing said coating composition on said side of said web inits said minor portion while thus yieldably supported by said positivegas pressure on the opposite side thereof.

3. In a method of smoothing mobile and dryable coating composition onone side of a flexible web, the steps of continuously advancing the webwhile maintaining the opposite side thereof in engagement with a guidesurface, urging a portion of said web away from said guide surface bymaintaining a pressure difference of a gas on opposite sides of saidportion of said web, smoothing said coating composition on said one sideof said portion of said web, and heating at least part of said gas tohelp dry said coating composition.

4. In a method of smoothing a mobile and dryable coating composition onone side of a flexible web, the steps of continuously advancing the saidweb in a fixed path by carrying the opposite side of said coated web ona perforate guide surface, maintaining a partial vacuum in back of amajor portion of said moving guide surface to retain said web againstsaid surface, urging a minor intermediate portion of said web away fromsaid moving guide surface by maintaining a cushion of positive gaspressure between said guide surface and said opposite side of said minorportion of said web, smoothing said coating composition on said one sideof said minor portion of said web, and heating the gas forming saidcushion to simultaneously help dry said coating composition.

5. Apparatus for coating flexible sheet material comprising, a perforateguide surface, smoothing means positioned in closely spaced relationshipto said guide surface, means for applying coating to one side of a webof the material, means for continuously advancing the web while itsother side is in engagement with said perforate guide surface, means toapply gas having a pressure difference on opposite sides of said web andthrough a portion of said guide surface to displace a portion of saidweb away from said guide surface and urge it into yieldable andoperative relationship with said smoothing means, and means coactingwith said guide surface and said displaced portion of said web to retardthe loss of said gas pressure difference.

6. Apparatus for coating flexible sheet material comprising, a perforateguide surface, a smoothing means positioned in closely spacedrelationship to said guide surface, means for applying coating to oneside of an elongated web of the material, means for continuouslyadvancing the web while its other side is in engagement with saidperforate guide surface, means to apply a pressurized gas through aportion of said guide surface under a portion of said web to displace itaway from said guide surface and yieldably urge it against saidsmoothing means, and dam means positioned adjacent each side edge of thetraveling web and coacting with said guide surface and said displacedportion of said web to retard the escape of pressurized gas so as toform a pressurized gas cushion under said displaced portion of said web.

7. Apparatus for coating flexible sheet material comprising, a rotatingcylinder having sides forming a perforate moving guide surface, asmoothing blade positioned in closely spaced relationship to said guidesurface, means for applying coating to one side of a web of material,means for continuously advancing said web while the other side thereofengages and moves with said perforate surface, a pressurized air chamberwithin said cylinder, said chamber having an outlet positioned to applypressurized air through a portion of said perforate surface of saidcylinder to displace a portion of said web away from said guide surfaceand urge it against said smoothing blade, and means coacting with saidcylinder and said displaced portion of said web to retard the escape ofpressurized air from beneath said web so as to form an air cushion undersaid displaced portion of said web.

8. Apparatus for coating flexible sheet material comprising, a perforateguide surface defining a convexly curved fixed path, smoothing meanspositioned in closely spaced relationship to said guide surface, meansfor applying coating to one side of said web material, means forcontinuously advancing said web while the other side thereof is inengagement with said convexly curved perforate guide surface, means toapply a pressurized gas through a portion of said guide surface todisplace a portion of said web away from said guide surface and urge itinto operative relationship with said smoothing means,

vacuum means to apply suction through other portions of said guidesurface adjacent to, and on both sides of, said pressurized portion toretain the web on said convexly curved guide surface, and means coactingwith said guide surface and said displaced portion of said web to retardthe escape of pressurized gas so as to form a gas cushion under saiddisplaced portion of said web.

9. Apparatus for coating flexible sheet material comprising, means forapplying coating to only one side of a web of the material, moving meansfor engageably supporting and continuously advancing said web, smoothingmeans adjacent only said one side, and means to urge a short length ofsaid advancing web away from said moving means and into operativerelationship with said smoothing means including gas cushion formingmeans maintaining a gas pressure difference on opposite sides of saidadvancing web to yieldably support it in said operative relationshipwith said smoothing means.

10. Apparatus for coating flexible sheet material comprising, means forapplying a dryable coating to one side of a web of material, movingmeans for continuously engaging and advancing said web, smoothing meansadjacent thereto, means to apply a pressure difference of heated gas onopposite sides of said web to urge it away from said moving means andinto operative relationship with said smoothing means while helping inthe drying of said coating.

11. Apparatus for smoothing a soft deformable coating already on anelongated sheet of flexible web material comprising, moving means forcontinuously, engaging, guiding, and moving said web, smoothing meansadjacent thereto, means including a gas chamber to apply a pressurediflerence of gas to the opposite sides of only a limited length of saidmoving web adjacent to said smoothing means to yieldably move it awayfrom said moving means and yieldably support said moving web inoperative engagement with said smoothing means.

References Cited in the file of this patent UNITED STATES PATENTS

1. A METHOD OF SMOOTHING MOBILE COATING COMPOSITION ON ONE SIDE OF AFLEXIBLE WEB COMPRISING, CONTINUOUSLY ENGAGING A MOVING SURFACE WITH THEOPPOSITE SIDE OF SAID COATED WEB TO ADVANCE SAID WEB ALONG A PATHDEFINED THEREBY, YIELDABLY MOVING A LIMITED LENGTH OF SAID ADVANCING WEBAWAY FROM SAID MOVING SURFACE AND HELD WITH ITS COATED ONE SIDE PRESSEDAGAINST A RIGID SMOOTHING ELEMENT BY GAS PRESSURE ACTING ACROSS SAIDLIMITED LENGTH OF SAID WEB TO THEREBY SMOOTH SAID COATING COMPOSITION ONSAID ONE SIDE OF SAID WEB WHILE IT IS YIELDABLY SUPPORTED BY SAID GASPRESSURE.